A variety of thermoplastic containers, such as containers for food and beverages, are well known in the art. Such thermoplastic containers are relatively inexpensive and disposable; and therefore are extremely popular. Such containers are often used at parties, picnics, gatherings, and other occasions where minimal clean-up is desired.
Containers made of thermoplastic materials are particularly advantageous for both manufacturers and consumers. Such containers are generally more durable than paper containers, yet inexpensive, lightweight, and recyclable.
Thermoforming generally begins with a thin sheet or web of material such as polyethylene, polypropylene, polyester, or polystyrene having a thickness within a range of from approximately 8 mils to 100 mils, depending on the size of the container to be manufactured. Cups and similar articles are typically made from plastic sheet or web having a pre-thermoforming thickness from approximately 30 to 60 mils, but the finished articles may be thinner after thermoforming. The sheet or web is heated to a temperature suitable for thermoforming—such as, for example, in a range from approximately 110° C. to about 200° C. for the above-mentioned materials—and is thereafter fed into a conventional forming assembly in which the process proceeds under applied positive and/or negative air pressure conditions. Depending on the thermoforming process, whether melt phase or solid phase, oven temperatures can vary and can reach up to 485° C. in melt phase thermoforming. A mold cavity is used to impart a particular shape to define the thin-walled container as the plastic sheet or web is drawn into the mold using vacuum pressure on one side of the sheet or web and/or a positive pressure on the opposite surface of the sheet or web. A plug assist can be used to aid in the process of imparting a particular shape to define the thin-walled container. The container generally includes a sidewall, and may also be provided with a rim or lip along the mouth of the container. The shape of the container may be decorative, but generally has a particular utility—e.g., ribs for strength, texturing for grasping, and formations for nestability in addition to other utilities. The processing period for a normal thermoforming operation can be between 1 and 20 seconds.
One disadvantage of many existing thermoformed cup and container designs is the lack of structural integrity in the sidewall and the rim. Sidewalls and rims of thin-walled thermoformed containers often bend and deflect inward easily. A deflection of this sort may constrict the volume of the container or cause spillage and overflows. Additionally, deflection of the sidewall can make the container more difficult to grip, as well as potentially leading to cracking of the container sidewall.
An additional disadvantage of many existing cup and container designs is that if provided, the rim may have a squared-off edge. Such a rim is not preferable because the sharp edges of the squared-off edge may be uncomfortable to the touch and germs may collect under the rim when it is not completely rolled, rendering it unsanitary. Alternatively, rolled rim configurations eliminate the disadvantages of squared-off rims or flanges, as well as add rigidity to the overall rim. A rolled rim on a container can additionally improve the fit of a lid onto the container rim.
A rolled rim can add significant rigidity to the rim as well as to close the space created at the rim. Such rolled rims have been created in containers formed of alkenyl aromatic polymeric materials such as polystyrene. There are numerous reasons, such as cost and consumer preference, to make consumer containers out of polyolefin polymer materials. However, polyolefin polymer materials become significantly softer than do alkenyl aromatic polymers during the thermoforming process. Due to the softness of polyolefin polymer material during thermoforming, such materials are not conducive to rim rolling processes. Thus, a need further exists for a blank for a container having a rolled rim that can be formed of a polyolefin material.
The present invention provides a solution to the recognized problems. The present invention is intended to provide a suitable blank for a container having a rolled rim made of polyolefin material, and a method for forming the same.